«It moves with the Splinter, it follows it around the circle.»
«Its direction rotates?»
«Yes.»
«So what happens to the Null Line, which is always perpendicular to it?»
Roi tapped her carapace in self-reproach. «The Null Line rotates! With each orbit the Splinter makes, the Null Line itself rotates.»
Zak said, «Yes. So the Splinter doesn't simply travel around this circle, it's also
turning
as it moves. It rotates around the shomal-junub axis, in exactly the same time it takes to make an orbit. If it wasn't doing that, there would be no Null Line: we would not be weightless anywhere, except at a single point, the center of the Splinter.»
Roi was growing dizzy. First the Splinter was flying through the Incandescence in a giant circle, now it was spinning as it went. «What about the first experiment, though? The one where you spun the tube and the stone gained weight?»
«Yes?» Zak sounded pleased that she'd raised this. «Tell me what that means for the Splinter.»
«We're on the Null Line, but I'm sure we're not precisely at the center of the Splinter. So we're spinning around the center, just like that stone. So why don't we have weight from that spin?»
«I believe we do. But it's balanced by something else.»
«What?»
Zak said, «Suppose we're thirty-six spans rarb along the Null Line from the center of the Splinter. If we're spinning around the center, which way should our weight point?»
«Rarb. Away from the center.»
«But we feel no weight at all. So if you
took away
the spin, then which way would our weight point?»
«In the opposite direction,» Roi supposed. «Back toward the center of the Splinter.»
«Right. Now, if we were thirty-six spans
shomal
of the center, which way would our weight point?»
Roi was confused. «Are we spinning now, or not?»
«It makes no difference. The spinning stone had no weight in the direction of its axis. Spinning the Splinter along the shomal-junub axis has no effect on weights in that direction.»
«All right,» Roi said, «then nothing has changed. Our weight would point back toward the center of the Splinter.»
Zak said, «So for any direction other than garm or sard — the directions that take us closer to, or further from, the center of the orbit — our weight would point toward the center of the Splinter itself. And what's more, if you look closely at the calculations, the weight at any given distance from the center of the Splinter would be equally strong, whether you traveled rarb, sharq, shomal or junub. Shomal-junub weight depends on the time for the Splinter to make one orbit, and your distance from the Null Line, in exactly the same way as the weight from spinning depends on time and distance. So if you took away the spin, shomal-junub weight and rarb-sharq weight would be exactly the same.»
Roi said, «Where does that leave the garm-sard weight?»
«You tell me. If the spin was absent, would the garm-sard weight be less or more?»
Spin produced weight away from the center, and the garm-sard weight itself was also away from the center, so part of it could be attributed to the Splinter's spin. «Without the spin, it would be less.»
«Yes,» Zak said. «Less, per span, by exactly the shomal-junub weight.»
«So if it was three times the shomal-junub weight with the spin, then without the spin it would be two?» Roi ventured.
Zak chirped with delight. «Yes! And
that
is what makes three beautiful. With spin, we can say the weights for the shomal-junub, garm-sard, and rarb-sharq axes are: one toward the center of the Splinter, three away, and zero. But the hidden picture, if we strip away the complication of the spin, is: one toward the center, two away from it, and one toward it again.»
«I can see that garm and sard are special,» Roi conceded. «But why should the garm-sard weight be exactly twice the others?»
«Because that gives a perfect balance between the amount of squeezing and the amount of stretching. Take a package of resin and squeeze it in two directions; I promise you, it will burst out in the third direction, with twice the force. It's not free to do anything else.»
Roi pondered Zak's mundane analogy for the arcane symmetry he was proposing. She could see the appeal of it, but was that really enough to determine all the laws of weight and motion?
She said, «What if the reality, with spin included, is two, not three? Then without spin, all the weights would be equal in size, but the garm-sard weight would be opposite the others. Wouldn't that be simple, too?»
«Perhaps,» Zak conceded. «Perhaps it's too much to hope for the geometry of weight to match the geometry of resin.»
«What we need to do,» Roi said, «is find some way to check. The map told us one thing, but our own weight measurements disagreed. We have to find another test, another measurement we can perform that will settle the question.»
Zak made a sound of concurrence, then sank into contemplation. Roi looked around the chamber. How long had passed since she'd entered? A whole shift? She was hungry, but reluctant to move, reluctant to break her connection to Zak. The most important thing now was their work.
He'd done it, she realized. All alone, without team-mates, with nothing but words, a couple of machines, and some simple ideas.
She was not going back to the crops on the edge. He'd hijacked her loyalty. He'd recruited her.
7
The first thing Rakesh saw upon opening his tent was Parantham, seated in a chair, in human form. Her detailed appearance was not the same as that which he'd assigned to her back in the node, but her identity signal ensured instant recognition. As he stepped out of the tent he tensed his forearm; his body believed it was real flesh. A moment's further introspection told him that he was not modifying his perceptions in any way. As far as he could tell he was simply seeing her as she was.
Parantham said, «Welcome to the bulge.» She was even speaking in his own native tongue.
«Thanks.»
She must have noticed his puzzlement, because she explained, «I thought it would make things simpler for our hosts if they only had to deal with one phenotype and one language.» She gestured at the instruments around them, which Rakesh had barely begun to take in. «Lots of hand-and-eye-driven interfaces, so it looks as if I made the right choice.»
Rakesh told his tent to fold itself. They were in a large cabin, inside some kind of space habitat; a window looked out on to a densely packed field of stars, slowly turning, suggesting a centrifugal origin for the gravity he felt. They'd requested exactly the same destination address as Lahl, but her metabolic and ergonomic needs would have been very different, so their hosts must have undertaken some extensive reconstruction. Rakesh had no idea what the Aloof would have done if Parantham had asked to be embodied as a blind limbless blob: maybe piped all the data straight into their minds, which would have been useful. Then again, maybe their hosts would have split them up, requiring them to take turns to examine the meteor with different instruments tailored to their different bodies.
The meteor itself was prominently displayed in the middle of the cabin, encased in a transparent enclosure, protected from contamination. As Rakesh walked over to it Parantham joined him. The object that had brought them all these thousands of light years was a dark gray slab of basalt about four meters across, its surface pitted with small impact craters.
He said, «What do the Aloof think we can do with this, that they can't do themselves?»
«Give a damn?» Parantham suggested.
«They cared enough to summon us here.»
«That wasn't difficult,» she said. «Though it might not be a question of effort; it might be a matter of what they see as appropriate. They might believe that they have no right to mess with this themselves, but we're entitled to know about it, and make of it what we will.» She smiled. «Though maybe that only applies to you, as molecular next-of-kin.»
They left the cabin and circumnavigated the habitat, a spinning ring some two hundred meters across. The main corridor led them to a kitchen, storerooms, a bathroom, two bedrooms, an exercise room, and a workshop. It was both gratifying and slightly chilling to see how well the Aloof understood the human phenotype's needs. The fixtures all had a generic quality, rather than the look of something made by humans for humans, but many cultures within the Amalgam would not have done a better job. Rakesh had swallowed a library before they'd left Massa, so it was a moot point as to whether his hosts had read his mind as the source of all this, or had studied other unencrypted human travelers on their way through the bulge, but they certainly hadn't shaped this place from his own memories; there was nothing specific to the culture of Shab-e-Noor, and they hadn't covered the walls with portraits of his family or lovers. They really couldn't win, though, because such tact itself invited its own creepy sense of invasiveness: they'd peered inside him deeply enough to understand how wrong that would have been.
If Rakesh felt naked, he had nobody but himself to blame. He'd known from the moment Lahl had offered him the key exactly how vulnerable he'd be, and he'd poured scorn on his friends' concerns. These were the terms, this was the deal; it was too late to have second thoughts. In principle, the possibilities for abuse were endless: the Aloof could be systematically torturing a billion helpless Rakesh-clones at this very moment. When he'd mentioned this primal fear to Parantham back on Massa, she'd pointed out that, while she'd regret the Aloof making anyone suffer, they could easily construct
de novos
of their own from scratch in order to mistreat them; sufficiently deranged sadists could always manufacture someone to torture, removing any need to lure their victims into a trap. In any case, Rakesh decided, there was nothing to be gained now from such paranoid speculation. Having handed their minds and bodies to their hosts as open books, the only sensible strategy that remained was to take their pleasant surroundings at face value and assume that the Aloof's hospitality, however narrowly defined, was genuine.
Back in the meteor room, they set to work. Rakesh had never had reason to be much of a materials scientist or ejecta expert before, and as he invoked the aid of the library the knowledge that flowed into him brought a thrill of discovery, a sense of new vistas opening up before him, that stretched far beyond his immediate needs. Imbibing a massive bolus of pre-digested information was not his usual means of educating himself — he much preferred the slow process of building incrementally on his own prior knowledge, testing and interpreting every assertion before accepting it — but there was no denying the rush of suddenly having thousands of new facts and insights jostling in his skull.
The equipment the Aloof had given them could probe the meteor's surface down to an atomic level; elicit and analyze emissions across the spectrum from gamma rays to microwaves; tomograph it in a thousand different ways; strike it, tap it, pound it, tickle it, and listen to the harmonics as it rang like a bell. Its gross chemical composition and its rarest impurities, its crystalline microstructure and the subtlest deformations thereof, were there for the asking. This rock, Rakesh thought, was as naked to them as they were to the Aloof.
He and Parantham collaborated efficiently, discussing the best strategies for the investigation, speaking a dense specialist lingo that would have been foreign to them both just minutes before. The primary interface to all of the instruments was a touch-screen console, but mercifully they weren't limited to reading the screen and tapping menus; the Aloof had tailored the interface to their detailed embodiments rather than a generic notion of the ancestral human phenotype, and the console could exchange data with the infrared ports in their fingertips.
Tomography alone was enough to locate the dead microbes, but it was necessary to send nanomachines crawling through the crevices to extract reliable DNA sequences. A dose of paleogenetic expertise from the library left Rakesh with no doubt that Lahl had been correct: these were not the corpses of any micro-organism, from any epoch, from any of the known DNA worlds. Their ancestors had probably been blasted off one of those planets billions of years before, on an entirely different piece of rock; that earlier meteor must have fallen to the ground somewhere in the bulge, and seeded a whole new biosphere. A billion or so years later this lump of basalt had been flung into the sky; with better luck it might have contributed to the DNA panspermia itself, but it was a dead seed now. At least, no pristine world could have revived these desiccated, shocked, radiation-fried microbes, though perhaps if they'd achieved the unlikely fate of landing on a planet already awash with DNA-based life, the right species of distant cousin might have scavenged a few of these corpses' gene fragments and tried them out for new ideas.
«The question now,» said Parantham, «is how do we find the parent world?»
The DNA sequences were enough to assign probabilities to the meteor's «grandparent world»: the planet out in the disk whose ejecta had seeded the world from which this rock had been blasted. Even those probabilities were not sharp, though; there were seven candidates that were almost equally likely. Given the chaotic dynamics of the bulge, this did not do much to narrow the search.
If the DNA couldn't help them, what of the rock itself? Three billion years before, lava flowing to the surface of the parent world had cooled into crystals of olivine, a magnesium-iron silicate, and augite, in which calcium, aluminum and titanium were also present. Subtle deformations in the structure of these crystals offered a partial history of the temperatures and pressures experienced by the rock since then.
The sudden heat and shock of the impact that had thrown the rock into space had left distinctive chemical fingerprints as well as physical dislocations. Over time, in the cool of the interstellar vacuum, some of the substances forged during the rock's fiery ejection had slowly decayed, hinting at a date for the event: fifty million years before. At the same time, the high-energy cosmic rays that flooded through the bulge from a myriad of sources had corroded the meteor's surface, left chemical deposits of their own, scoured tracks deep inside the rock, and created trace amounts of new isotopes. As Lahl had claimed back in the node, both lines of evidence converged on the same date: the rock had apparently drifted through the bulge, unprotected by any atmosphere or planetary magnetic field, for about fifty million years.